1. Field of the Invention
The present invention relates to explosive formulations containing halogenated wax binder systems and process for production thereof, the process involving dilution of the halogenated wax in a non-aqueous lacquer, slurring fine and very fine particle size crystalline explosive in an aqueous solution, adding the lacquer, distilling off the solvent, vacuum filtering and drying to yield a granular explosive which provides complete coating to avoid hot spots and is easily pressable at lower temperature and pressure.
2. Discussion of the Prior Art
Newer munitions are designed to minimize any violent (explosive) response when subjected unintended stimuli during transportation, storage, or because of enemy action. It is also critical that such Insensitive Munitions (IM) not sacrifice necessary explosive efficiency of the conventional munitions they replace.
Denser explosives generally yield higher detonation velocities and pressures, i.e. greater explosive efficiency. Particularly high efficiency explosives that are chemically stable and relatively safe to handle are aliphatic nitramines, including cyclotetramethylenetetranitramine, HMX, and cyclotrimethylenetrinitramine, RDX. HMX is an efficient explosive, having a detonation velocity above 9,000 m/sec. (at a density of 1.9); RDX exhibits a detonation velocity of 8,400 m/sec. (at a density of 1.7); while TNT exhibits a detonation velocity of 6,940 m/sec. (at a density of 1.62).
TNT has a melting point of 80° C., such that it can be cast or easily pressed into the desired shape. It contrast, HMX has a melt point of 282° C. and RDX has a melt point of 203° C., such that these explosives would decompose if cast. Further, it has long been known that crystalline organic detonating compounds such as RDX, and HMX, must be treated with an additive to impart to them the characteristics required for handling and processing. When untreated, the discrete particles comprising these materials generally have poor flowing properties which tend to make the particles bridge deleteriously during their introduction into munitions. Furthermore, due to the lack of cohesive forces among these discrete particles, the plain or untreated, RDX or HMX cannot be pressed into pellets or the like, for example those used in shape charges, of sufficient coherency to maintain their form when removed from the die or when subjected to the usual mechanical stresses incurred in handling.
To provide the necessary free-flowing properties, crystalline organic explosives are usually treated with a graining agent, i.e. an additive imparting free flow, which coats and lubricates the larger grains and agglomerates the finer crystals. Numerous graining agents are known, including graphite, wax, gums, shellacs, polyvinyl alcohol, and a variety of plastics and resins. In many instances these graining agents act also as binders which facilitate the forming of the crystalline explosive into a coherent mass. One particular pressed explosive charge is disclosed in U.S. Pat. No. 3,291,666, which discloses admixing a copolymer of vinylidene fluoride and hexafluoropropylene with the crystalline explosive to obtain a free flowing, readily pressable composition. A second pressable explosive is disclosed in U.S. Pat. No. 5,547,526, which discloses a pressed plastic bonded explosive that is pressed under a pressure of 1000 bar (˜14,500 psi) or higher.
As stated above, explosive formulations may contain wax binders, such as the combination of carnauba max and ozokerite wax disclosed in U.S. Pat. No. 6,641,683. Such wax binder based formulations provide a matrix which can accept reactive metals to enhance the heat of reaction, while being cost effective, and easily loaded using high speed presses. Further, such wax binders phlegmatize, i.e. stabilize or desensitize, the explosive formulation, as the wax tends to fill in gaps between explosive grains, lowering the probability of unintended initiation, i.e. lowering the sensitivity. The extent of sensitivity reduction generally relates to the amount of wax included in the formulation. However, addition of wax strongly reduces explosive performance, again in proportion to the amount of wax added. Thus, there is a tradeoff between increasing the amount of wax to obtain better insensitivity with reduced performance and decreasing the wax to gain higher power at the cost of becoming more sensitive.
In December 2006, at the Joint Army, Navy and Air Force (JANNAF) 41st CS129th APS/23rd PSHS, in San Diego. P. Samuels, S. Singh, and B. Fishburn, disclosed use of halogenated wax binder systems in high power explosives. A developmental PAX-46 explosive was disclosed, containing 91.5% bi-modal RDX, 8.5% chlorinated wax and oil, i.e. a plasticizer. This RDX/chlorinated wax based explosive was disclosed to exceed the IM properties of LX-14, containing 95.5% HMX and 4.5% plastic binder system. PAX-46 was said to yield greater explosive efficiency than Composition A5, a RDX/stearic acid based explosive used in numerous munitions, including guided multiple launch rocked systems (GMLRS), 40-mm M430A1, assorted submunitions, small shaped charges and boosters. However, the December 2006 disclosure failed to disclose anything regarding the manufacture of PAX-46 or similar halogenated wax binder explosives; failed to disclosure anything specific about the binders system, e.g. other than usage of wax and oil combination, nothing was said about a particular solid/liquid binder system; failed to disclose anything about the particle size of the explosive material; failed to mention anything about hotspots; and with respect to flow properties, only mentioning that PAX-46 was durable to help in pressing, and had good flow properties.
U.S. Pat. No. 6,641,683, mentioned above, discloses a melt process for the manufacture of wax based explosive compositions, which results in a castable product. However, this process does not yield pressable granules amiable to modern high speed pressing into shaped charges, warhead explosives, or shell propellants. Also, the melt process of U.S. Pat. No. 6,641,683 subjects the composition to temperatures of from 84° C. to 820° C., which high temperatures can cause undesirable softening, agglomeration and potential degradation of the subject halogenated wax binder explosive, all of which will negatively effect its flow properties, if it were desired to attempt to press the resulting product into finished munitions.
U.S. Pat. No. 3,985,595 discloses a heat resistant symtriaminotrinitrobenzene (TATB) explosive composition that contains a halogenated plastic (i.e. fully saturated copolymer of chlorotrifluoroethylene and vinylidene fluoride) binder, which is manufactured by a known slurry process resulting in explosive beads, which beads form a moldable powder. This slurry process involves mixing powdered explosive and water in a kettle equipped with a condenser and agitator. A lacquer composed of the halogenated plastic is dissolved in a suitable solvent and added to the slurry. The solvent is removed by distillation, such as by use of a steam sparger, causing the plastic phase to participate out on the explosive. The resulting plastic-explosive agglomerates into “beads” as the stirring and solvent removal continues. The water is removed from the beads by filtration and drying, which drying is disclosed to be in a forced draft oven at 100° C. Unfortunately, this process, subjecting the composition repeatedly to elevated temperatures, such as with a steam sparger, giving localized temperatures well over 100° C., and subsequent 100° C. drying, can cause undesired softening and agglomeration of the subject halogenated wax binder explosive and as stated above, negatively impact its flow properties. Further, the U.S. Pat. No. 3,985,595 discloses a preference to reduce agitation during the solvent removal step, an act which is contraindicated with halogenated wax binder explosives due to a phase separation unique to such systems, as discussed below.
There is a need in the art for a halogenated wax binder explosive and means for manufacture thereof, the explosive having good flow properties and good pressability, required for modern munition high speed manufacturing, as well as, uniform coating to avoid hot spots.